its called hackintosh. i think its pretty complicated unless you know what you doing lol.

http://www.hackintosh.com/

from their site if you scroll down a bit:

You can't just shove a Mac OS X DVD into any old PC and expect it to work like it does on a Mac. Let's face it, given the vast assortment of configurations, you can't put a Windows DVD into any old PC and expect it to work like Mac OS X does on a Mac. Fortunately, many have experimented with Mac OS X on a wide variety of PC hardware and have shared their findings with the world.